Question 181451
Let {{{a}}} = the number of packs of 12 oz cups she bought
Let {{{b}}} = the number of packs of 16 oz cups she bought
given:
(1) {{{a + b = 10}}}
(2) {{{180a + 240b = 2160}}}
Multiply both sides of (1) by 180 and subtract from (2)
(2) {{{180a + 240b = 2160}}}
(1) {{{-180a - 180b = -1800}}}
{{{60b = 360}}}
{{{b = 6}}}
and, since
(1) {{{a + b = 10}}}
{{{a + 6 = 10}}}
{{{a = 4}}}
She bought 4 packs of 12 oz cups and
6 packs of 16 oz cups
check answer:
(2) {{{180a + 240b = 2160}}}
(2) {{{180*4 + 240*6 = 2160}}}
{{{720 + 1440 = 2160}}}
{{{2160 = 2160}}}
OK